The invention relates to a method for evaluating process characteristics of injection-molding tools in the sense of qualitatively and/or quantitatively classifying injection-molding tools in tool categories. Building thereon, a determining of preferred intervention ranges and/or manipulated variables is presented for adapting injection molding machine parameters in the case of changing ambient conditions and/or determining the influence of disturbing effects on an injection-molding process.
An ideally adjusted injection-molding process of an injection-molding machine with a particular tool for the production of a particular shaped part is subject, in cyclic operation, in reality to fluctuations continuously, which are due to changing ambient conditions and/or to the influence of disturbing effects on the injection-molding process. Such changing ambient conditions can be, for example:                changing hall temperature in the factory hall, in which the injection-molding machine is set up. Thereby, changed heat loss flows from the tool or from the heating devices of the injection-molding machine into the environment can occur, which in turn can have a direct influence on the temperature of the melt and therefore on its viscosity.        quality fluctuations of the raw material which is to be processed, wherein fiber content, humidity or regranulate content of the raw material can change for example from load to load, which likewise can bring about viscosity changes to the melt with fixedly pre-set injection-molding machine parameters.        
Hereby, considerable quality deviations of the produced shaped parts can occur. For example, an overfilling, i.e. an over-injecting, of the molding tool can occur, which on the one hand brings about undesired burrs on the shaped part and on the other hand can lead to damage to the molding tool. On the other hand, it can lead to a defective filling of the mold, which presents itself by shaped parts which are not completely molded, which likewise during the further procedure are to be categorized as rejects when the required quality standards are no longer achieved.
In order to compensate effects of changing viscosity of the melt over time, it is known to adapt the holding-pressure level on the basis of a pressure measurement in the tool cavity. Furthermore, it is known, for correction of changing viscosities, to adapt the moment and/or the position of the switchover from the injection phase into the holding-pressure phase, i.e. the establishing of the so-called switchover point. In the prior art, it is necessary here in both the above-mentioned methods, that an experienced, i.e. intensively trained machine operator firstly determines the type of the suitable intervention ranges and/or the suitable manipulated variables on the basis of the knowledge of the part which is to be produced and thereby on the basis of the knowledge of the tool cavity and its characteristics. In a second step, the experienced machine operator is required, after he has selected a suitable type of manipulated values or intervention ranges which are to be influenced, additionally on the basis of his experience to establish the extent of the intervention or the extent of the changes which are to be carried out, in order to again obtain a qualitatively good shaped part. This is founded in that the expedient selection of intervention ranges and/or manipulated variables and also an extent of a respective intervention is highly dependent on the geometry of a respective part which is to be produced, for example a very thin-walled or a rather thick-walled shaped part and the quality fluctuation of the raw material and/or of the raw material type. Thus, for example, in the case of a relatively thin-walled component, i.e. in the case of a relatively thin-walled tool cavity, in which solidification processes of the melt occur very quickly, it is little effective to increase the holding pressure or to extend the holding pressure duration. Rather, the injection speed is more promising here for an expedient selection of the intervention range, in order to ensure that the molding tool is filled as completely as possible or the filling volume is withdrawn somewhat in the case of an over-injecting.
For such a change to the injection-molding machine parameters and their basic selection, an experienced machine operator is imperatively necessary in the prior art, who, on the basis of his knowledge and skill selects constructive intervention ranges and/or manipulated variables and corrects these with regard to their extent. It is disadvantageous here that a complete automation of the injection-molding process is not possible, because in the case of changing ambient conditions or the occurrence or influence of disturbing effects on the injection-molding process an intervention by an experienced machine operator is imperatively necessary.
As a basis for an optimizing intervention, inter alia a pressure measurement is carried out in the tool cavity. However, this has the result that an additional pressure sensor is required in the tool cavity. With regard to such a pressure sensor, it has been found that the latter, on the one hand, is cost-intensive to install and produces high maintenance requirements within the tool maintenance.